Predicted grades - mock exam stress

I'm currently in the middle of my Year 12 mock exams.

I'm not stressed about my other two subjects because my teachers have seen that I'm capable of doing well, but I'm worried about Geography. In November and January I got 2 D's in one topic, in February I got a B in another one and in March I got a B in my third topic, but I feel like my teachers really aren't aware of my potential.

I've been told that whatever I get in these mocks is going to pretty much be what goes on my UCAS form as my predicted grades, but that the teachers can move the grades up a bit if they feel like I can do better and this is what I'm worried about - I know for a fact that I can do better but they don't know this and haven't seen evidence of this. Has anyone who's been in a similar position got any advice?